1. Field of the Invention
The invention relates to a vibrating gyroscope.
2. Description of Related Art
Vibrating gyroscopes are currently used in numerous fields, especially because of their solidity, their reduced electrical consumption, and their rapid execution.
These gyroscopes comprise a resonator which can take various forms, such as a bell or a tuning fork.
The invention relates more particularly to resonators comprising a body of generally cylindrical shape.
The axis z is conventionally designated as the axis of the cylinder, the axes x, y being arranged in the plane orthogonal to the axis z.
It is known that such a resonator in vibration deforms itself preferably elliptically, with four vibration antinodes regularly arranged over the circumference of the cylinder in the plane x, y. A first vibration mode 53, 57 of the resonator is illustrated in FIG. 1, at two given instants, relative to its rest state 54. The resonator passes from ellipse 53 to ellipse 57 at the end of a semi-period, but this is still the same vibration mode.
Any rotation of the gyroscope about the axis z generates Coriolis forces which have a tendency to cause offset in rotation of vibration antinodes about the circumference of the cylinder. Piezoelectric detection elements, placed at the level of the vibration antinodes, measure a signal, the variation of which determines the angular rotation speed and/or the angle of rotation about the axis z.
It is known that vibration antinodes correspond to the maxima in amplitude of the vibration of the resonator.
By way of illustration, it is evident in FIG. 1 that rotation of the resonator causes secondary vibration in elliptical mode 52, 58 whereof the principal axes x1, y1 are located at 45° of the axes x, y. Vibration passes from ellipse 52 to ellipse 58 at the end of a semi-period.
The signal measured by the piezoelectric detection elements at the level of these axes especially determines the angular rotation speed.
More generally, the resonator 3 is capable of vibrating according to couples of modes whereof the antinodes are distributed on n axes, with n a whole number greater than or equal to two. Each of the couples of modes for each value of n has a sensitivity to the speed of rotation of the resonator and can be used to make a gyroscope. The case of n=2 corresponds to elliptical vibration modes, as illustrated in FIG. 1.
In general, gyroscopes comprise four piezoelectric detection elements for maintaining the vibration of said resonator, and four other piezoelectric elements for measuring the vibration signal of the resonator. These eight elements are most often arranged uniformly about the resonator (four on axes x, y and four on axes x1, y1).
It is known that parasite vibration modes appear in cylindrical resonators. These are for example the modes shown in FIG. 2: vibration mode 55, said drum mode, and vibration mode 56, said flexion mode.
Detection solutions of vibration modes proposed to date do not reject these parasite modes.
Therefore a solution for improving the devices of the prior art should be proposed.